1. Field of the Invention
This invention relates to a color toner for electrophotography, particularly, a color toner containing a specific compound as a coloring agent.
2. Description of the Prior Art
There are two types of systems for developing electrostatic latent images formed on an electrophotographic photosensitive material, electrostatic recording material and the like, one of which uses a liquid developer (wet type developing method), and the other of which uses a dry developer such as a one component type toner having a coloring agent dispersed in a binder resin or a two component type toner comprising a mixture of said one component type toner with a solid carrier (dry type developing method). These systems have merits and demerits. Recently, the dry type developing method, particularly a two component type developer has been generally used.
A toner conventionally used for the two component type developer is prepared by admixing a coloring agent (dye or pigment) with a binder resin, kneading the resultant admixture by a two-roll mill or other means in the melted state, and powdering the kneaded mixture to a particle size of 1.about.30 .mu.m. The toner thus prepared is mixed with a carrier material having a particle size of 50.about.100 .mu.m, thereby producing a developer used for developing an electrostatic latent image.
In order to use the toner and carrier for developing an electrostatic latent image, they must be constantly triboelectrified in a copier, and the triboelectrified toner having a stable electrified amount is then applied to the electrostatic latent image. Therefore, it is necessary for imparting the desired triboelectricity (i) to appropriately select a binder resin and/or a coloring agent for a toner, or (ii) to add a charge controlling agent (an agent for controlling the electricity of a toner against the friction with a carrier) to a toner.
However, even today, the selection of an appropriate binder resin in the above step (i) can not be satisfactorily carried out. For example, it is known to use a chlorinated paraffin, unsaturated polyester and the like as a binder resin for making a toner negatively electrified, or to use the specific polyester resin having a kind of cross-linking structure (reaction product of non-linear low melting aromatic resin with chelated salicylic acid), but these resins do not have a molecular weight suitable for a binder resin, thus not having appropriate heat-properties (appropriate melting properties by heat roll during fixing) desired for a toner. Therefore, these resins provide various problems such as copy delivery miss caused by the winding of a copy about a heat roll, and "off-set" phenomenon that a developed image becomes unclear because a toner on a copy paper is transferred to the surface of a roller.
In the selection of a coloring agent in the above step (i), examples of the conventional coloring agents proposed for a toner of a liquid developer include various kinds of dyes, for example, anthraquinone derivatives (ones having a long chain alkyl phenyl group, a long chain alkyl amino group or the like, laked or electrified ones, ones produced by reacting with a surface active agent, and acidic group containing water-soluble dyes having an anthraquinone group introduced) and the like. However, a satisfactory effect can not be achieved for a dry type toner, particularly a toner of a two-component type developer by these conventional dyes such as anthraquinone derivatives.
On the other hand, examples of the conventionally known charge controlling agents used in the step (ii) include an agent for imparting a positive charge to a toner such as a nigrosine type dye and an agent for imparting a negative charge to a toner such as a chromium-containing monoazo complex, metal complex of salicylic acid, chromium-containing salicylic acid compound complex, chlorine-containing organic dye (Copper Phthalocyanine Green, chlorine-containing monoazo dye), metal-containing dye of phthalocyanine type dye, nitrohumic acid (salt), and the like. However, most of these conventional charge controlling agents have disadvantages that they are blackish materials, that they have poor compatibility or wetting property with a binder resin, or that their charge controlling properties do not remain long because of a subliming property. Thus, most of them are unsuitable as a charge controlling agent for a color toner of electrophotography. Recently, a demand for producing a multicolor copy from a multicolor original has been increased year by year, but these conventional charge controlling agents can not satisfy this demand because of the above mentioned disadvantages. A toner containing these conventional charge controlling agents has favourable developing properties at the initial stage, but its life is short and environmental stability is poor (stability to the changes of temperature and moisture is poor). Therefore, there are defects that the density of a copied image is lowered and that fog, stain and the like appear on a copy paper.
The above mentioned conventional coloring agents and charge controlling agents are disclosed in Japanese Patent Publication Nos. 48-25941, 48-26784, 49-20225, 46-43440, 48-30899, 49-46423 and 49-26909, and Japanese Patent Laid Open Nos. 50-140137, 50-142037, 50-142038, 49-51949, 49-134303 and 60-46566.